Zeitschrift fur Geomorphologie, Vol. 61/4 (2018), 275-302 Published online March 2018; published in print June 2018 Open Access Article Returning to the facts: Response to the refusal of tsunami traces in the ancient harbour of lechaion (Gulf of Corinth, Greece) by 'non-catastrophists' - Reaffirmed evidence of harbour destruction by historical earthquakes and tsunamis in AD 69-79 and the 6 th cent. AD and a preceding pre-historical event in the early 8 th cent. BC Andreas VOtt1*, Hanna Hadler1, Benjamin Koster 2 , Margret Matthes-Schmidt 2 , Bjorn R. Robke 3 , Timo Willershauser1, Klaus Reicherter 2 1 Institute of Geography, Johannes Gutenberg-Universitat Mainz, Johann-Joachim-Becher-Weg 21,55099 Mainz, Germany 2 Neotectonics and Natural Hazards Group, RWTH Aachen University, Lochnerstr. 4-20, 52056 Aachen, Germany 3 Department of Applied Morphodynamics, Deltares, P.O. Box 177, 2600 Delft, The Netherlands * Corresponding author: voett@uni-mainz.de With 4 figures and 1 table Abstract: The ancient harbour of Lechaion supposedly was one of the most important harbours of the ancient world. Representing the western harbour of Corinth at the eastern end of the Gulf of Corinth, it was of major impor- tance for commercial trade and military purposes. This paper is a response to the article by Kolaiti et al. (2017) who reject recent findings by Hadler et al. (2011, 2013) and Koster et al. (2013). The latter presented evidence ofmul- tiple tsunami impact on the harbour. Kolaiti et al. (2017) reassessed and interpreted historical, archaeological and climatological data concluding that there is no evidence that tsunami waves inundated the Lechaion site and that the overall tsunami potential in the eastern Gulf of Corinth is comparatively low. Instead, environmental changes in and around the ancient harbour are supposed to have been controlled by climatological factors, such as wind, swell and sea currents as well as human interventions. In this paper, we re-evaluate and synthesize geomorphological, strati- graphical and geochronological data published by Stiros et al. (1996), Morhange et al. (2012) and Hadler et al. (2013) and consider seismo-historical information collected by Mourtzas et al. (2014) and palaeoseismological data by Minos-Minopoulos et al. (2015). Based on geoscientific facts, the main statements of Kolaiti et al. (2017) are evaluated. From an epistemological point of view, the rationale brought forward by Kolaiti et al. (2017) that tsu- nami impact is not acceptable as long as historical evidence is missing, is untenable. Tsunami traces in geological archives dated by means of absolute dating techniques must not be rejected because they are not included in exist- ing catalogues summarizing historical data. Earthquake and tsunami catalogues are known to be incomplete (Hadler et al. 2012, Papadopoulos 2015: 150). Based on original grain size data, we show that the sediment core from the central harbour basin drilled by Morhange et al. (2012) includes two tsunami candidate layers so far uurecognized. Moreover, the re-interpretation of vibra core data from Hadler et al. (2013) by Kolaiti et al. (2017) in terms of man- made intervention instead of tsunami-related impact is not consistent with available macro- and microfossil signa- tures. In order to achieve a consistent set of comparable radiocarbon data, we calculated the best-fit approximation of the local marine reservoir effect (MRE) for the Lechaion area as L'lR= 133 ± 75 for marine samples and used this new L'lRto re-calibrate all available radiocarbon ages published by Stiros et al. (1996), Morhange et al. (2012), Campos et al. (2013a, 20 13b) and Hadler et al. (2013). Bringing together ancient harbour chrono-stratigraphies and the seismo-tectonic history of Lechaion and its environs, the timing of tsunami event I identified by Hadler et al. (2013) can be refined to the 770s cal BC, i.e. the early 8 th cent. BC. This age is well consistent with the age of a homogenite-turbidite sequence described by Campos et al. (2013a, 2013b) from c. 42 km distant from Lechaion at 867 m water depth indicating an earthquake-triggered tsunami/seiche effect. The age of tsunami event II detected 001: 10.1127/zfg/2018/0519 © 2018 The Authors GebrOder Borntraeger Science Publishers, Stuttgart, www.borntraeger-cramer.com